1. Field of the Invention
This invention relates to a remain detector operated by a variation in pressure and a liquid injection recording apparatus provided with the detector.
2. Related Background Art
The liquid injection recording apparatus is usually called an ink jet recording apparatus, and is designed such that ink in a plurality of ink discharge ports provided in a recording head is driven on the basis of recording information, whereby flying ink droplets going from the ink discharge ports toward a recording medium are formed to record images, characters, etc. on the recording medium.
In the recording apparatus of this type, an ink ribbon or the like is not used, but rather, liquid ink stored in an ink tank is supplied to a recording head through an ink supply path formed by a tube or the like and is caused to fly as minute liquid droplets to a recording medium by the discharging mechanism of the recording head and adhere to the recording medium to thereby accomplish recording.
Accordingly, unlike an ink ribbon type recording apparatus, to prevent unsatisfactory recording caused by the shortage of ink, a construction is generally adopted in which a device for detecting the amount of remaining ink in the ink tank is provided and when the amount of remaining ink has become insufficient, an alarm sound or the like is generated to thereby urge the operator to supply ink or interchange the cartridge type ink tank.
FIGS. 1A and 1B of the accompanying drawings show the construction of the essential portions of liquid injection recording apparatuses which are suitable for applying the present invention.
In FIG. 1A, a recording head 1 is for discharging ink droplets to a recording medium having its recording surface regulated by a platen 8 to thereby accomplish recording, and is carried on a carriage 2 movable along a pair of guide shafts G installed parallel to the platen 8.
A sub-ink tank 4 is also carried on the carriage 2, and the ink in this sub-ink tank is supplied to the recording head 1 through a supply tube 3.
An ink tank 7, as an ink supply source, is mounted on the body side of the recording apparatus, and this ink tank 7 and the sub-ink tank 4 are connected together by a flexible ink supply tube 5A. The ink tank 7 is constructed of a flat and flexible bag member formed of a sheet of plastic material or aluminum. An ink remain detector 6 is connected in the ink supply tube 5A.
The flexible ink supply tube 5A is bundled with a flexible suction tube 5B from half-way thereof, and constitutes a flexible communicating member 5 for absorbing the movement of the carriage 2.
The suction tube 5B connects a pump (suction means) 9 to the sub-ink tank so that the liquid level in the sub-ink tank 4 is maintained within a predetermined range. Also, this pump 9 is connected to capping means 10 for hermetically sealing the recording head 1, and constitutes an ink recovering device for sucking the ink from the fore end (the ink discharge ports) of the head 1 when recording is unsatisfactory or when the ink tank 7 is to be interchanged.
In the construction of FIG. 1A, the ink stored in the ink tank 7 is directed to the sub-ink tank 4 on the carriage 2 through the ink remain detector 6 and the ink supply tube 5A. Further, the ink is directed from the sub-ink tank 4 to the recording head 1 through the supply tube 3, and is discharged from the ink discharge ports of the recording head on the basis of recording information, whereby recording is effected on the recording medium on the platen 8.
FIG. 2 of the accompanying drawings shows a structure proposed as the ink remain detector 6.
In FIG. 2, a flexible film member 13 is held between a body 11 and the joined surface of a cover 12, and the space in the body 11 provides an ink chamber 26 isolated from the atmosphere. The body 11, the film member 13 and the cover 12 may be jointed together by a suitable method such as bonding, welding or screw-setting.
The body 11 is formed with an ink inflow port 24 and an ink outflow port 25 for connecting the ink supply tube 5A (FIGS. 1A and 1B), and the ink chamber 26 which, being a space partitioned by the film member 13, forms a part of an ink supply path.
The film member 13 is supported between a lower plate 14 and an upper plate 15.
The lower plate 14 is coupled to the lower end of a bolt 17 biased upwardly by a spring 16, and is normally held in its uppermost position as shown.
On the other hand, the upper plate 15 is slidably fitted to the bolt 17 and urged against a pair of electrodes 18 and 19 fixed to the back of the cover 12 with the lower plate 14 and the film member 13 interposed therebetween, by the spring force of the spring 16. The upper plate 15 is made of an electrically conductive material and may be urged against and separated from the pair of electrodes 18 and 19 to perform a switching operation as detector means.
The electrodes 18 and 19 are connected to leadout terminals 20 and 21, respectively, provided on the cover 12.
A nut 22 is threadably engaged with the upper threaded portion of the bolt 17 so as to be adjustabIe in its vertical position, and the spring (compression coil spring 16 is mounted below the nut 22 between a spring holder 23 and the surface of the cover 12.
Thus, by rotating the nut 22 and adjusting the position of the nut 22 on the bolt 17 by adjusting means, which is screw means, the magnitude of the upward force of the spring 16 acting on the film member 13 can be adjusted, whereby the operation setting of the ink remain detector 6 can be adjusted.
In such a construction, when the amount of remaining ink in the ink tank 7 in the form of a hermetically sealed bag having at least a portion thereof formed of a flexible sheet decreases, the negative, pressure in the ink supply path becomes strong. In response thereto, the film member 13 is downwardly attracted against the spring force of the spring 16, and when a predetermined negative pressure value adjusted by the nut 22 is reached, the film member 13 lowers and the electrically conductive plate 15 separates from the pair of electrodes 18 and 19.
Thereby, the lead-out terminals 20 and 21 are switched off (rendered non-conductive) and by the then variation in resistance value, it is detected that the amount of remaining ink has become less than a set value.
However, the conventional ink remain detector 6 of FIG. 2 sometimes gives rise to the following problems.
If consumption of ink is continued by the recording operation or by using the pump even after it is detected that the amount of remaining ink has become less than the set value, excessively great deformation occurs to the flexible film member 13 due to the excessive negative pressure produced in the ink supply path. This has led to the possibility that the operation setting pressure is varied and further, the film member 13 is damaged.
Also, continued recording with the amount of remaining ink being null would adversely affect the recording head 1.
These inconveniences are liable to occur when the operator of the recording apparatus is absent in spite of the ink remain detector having operated during recording.
As means for preventing such inconveniences, it is conceivable to stop the operation of the recording apparatus when an output, detecting that the amount of remaining ink has become small, is produced from the ink remain detector.
However, this method suffers from the great possibility that the, record, becomes wasteful in the course of recording. Also it has not always been a suitable method to carry out if the recording time and the amount of consumed ink are taken into account, particularly when hard copies are being output in a color liquid injection recording apparatus.
Also, in FIG. 1B, there is shown another form of the liquid injection recording apparatus provided with the ink remain detector described with reference to FIG. 1A. The difference between the apparatus of FIG. 1A and the apparatus of FIG. 1B is that in FIG. 1A, the ink remain detector 6 is connected to the ink supply tube 5A, whereas in FIG. 1B, the ink supply tube 5A is communicated with the ink tank 7 and the ink remain detector 6 is communicated with the ink tank 7 discretely therefrom. Accordingly, the apparatus shown in FIG. 1B need not be described in greater detail. Of course, in the case of FIG. 1B, one of the outlets of the ink remain detector 6 is closed so that no ink may leak.
In the case of FIG. 1B, any fluctuation of the pressure of the ink remain detector 6 is not transmitted to the ink in the ink supply tube 5A. This leads to a good result with respect to stable recording and stable detection of the amount of remaining ink. However, even in the case of the form shown in FIG. 1B, the above-noted problems have not been solved.